The present invention relates to a semiconductor optical device using a mixed crystal consisting of IV-group semiconductors, a manufacturing method for it, and an opto-electronic integrated circuit using it.
IV-group semiconductors such as Si and Ge are indirect transition type semiconductors. Therefore, they have a very low light emitting efficiency and are not suited for use in light emitting devices. However, it has been found recently that a mixed crystal of SiGe emits light strongly by photoluminescence though at a low temperature. Since it was announced in J. C. Sturm et al; Physical Review Letters, Vol. 66 (1991), pp. 1362-1365, a light emitting device using SiGe has been studied enthusiastically.
A light emitting device has a layered structure where Si and a mixed crystal of SiGe are put on top of each other and a layer of Si is placed on the top. The mixed crystal of SiGe is a light emitting region. Light emission occurs because Ge atoms in the SiGe crystal occupy crystal lattice sites of Si at random, so that the translation symmetry of the Si crystal is lost and the band structure is changed.
According to the above prior art, the band discontinuity of the conduction band between the Si barrier layer for confining carriers and the SiGe well layer is extremely low such as about 20 meV and electrons cannot be confined effectively at room temperature, so that devices which operate efficiently at room temperature cannot be formed,
Furthermore, a method to manufacture light emitting and sensing devices constructed from IV-group semiconductors such as Si and Ge is also discussed in X. Xiano et al; Applied Physics Letters, Vol. 60, Number 14 (1992), pp. 1720-1722.
According to X. Xiano et al, a light emitting phenomenon caused by recombination of electrons and holes which are confined in the quantum well Si.sub.1-W Ge.sub.W (w=0.2) having the Si/Si.sub.1-W Ge.sub.W (w=0.2)/Si structure is observed. However, the band discontinuity of the conduction band between Si and Si.sub.1-W Ge.sub.W (w=0.2) is extremely low, about 20 meV as mentioned above, and electrons cannot be confined in the quantum well at room temperature: photoluminescence can be observed from the quantum well only at a low temperature such as about 77K.
In the case of the structure of X. Xiano et al, it is considered to decrease the band gap (forbidden band width) and increase the band discontinuity by increasing the w value of Si.sub.1-w Ge.sub.w. However, in this structure, as the band gap decreases, only the band discontinuity of the valence band increases but the band discontinuity of the conduction band does not increase. Therefore, although holes can be confined in the Si.sub.1-w Ge.sub.w layer, electrons cannot be confined at room temperature and efficient light emission at room temperature is not reported.
On the other hand, in a conventional opto-electronic integrated circuit, light emitting devices are made of III-V compound semiconductors and electronic elements are made of Si. Therefore, it is difficult to form light emitting devices and electronic elements in a chip.